Fast opening switch



M. BENDER ETAL FAST OPENING SWITCH Filed Dec.

Sept; 17, 1963 FIG. 2 .i'.

FOIL HOLDERS d C LEVEL 4 i-lOO psec OF BA\T\T9ERY TO OSCILLOSCOPE ZERO VOLTS WHEN RELAY OPENED THE CIRCUIT FIG. 5

FIG.4

INVENTOR.

MAX BENDER BY FRANK K. BENNETT ARTHUR F. KUCKES United States Patent 3,104,255 FAST OPENING SWITCH Max Bender and Frank K. Bennett, Trenton, and Arthur F. Kuckes, Princeton, N.J., assignors to the United States of America as represented by the United States Atomic Energy Commission Filed Dec. 6, 1961, Ser. No. 157,607 9 laims. (Ci. 200-87) This invention relates to electrical switches and more particularly to a novel and improved fast acting switch of the magnetic actuated type.

Many industrial and research apparatuses require the operation of fast-acting switches for opening a circuit carrying electrical energy. In plasma research reactors of the stellarator class, for example, where a high energy source has been used to energize an ohmic heating circuit with high voltages and currents of up to 1000 amperes or over for predetermined times, it has been necessary, after the elapse of the time interval, to open the circuit with a switch that has disconnected the energy source from the ohmic heating coil in a very short time.

Conventional mechanical or magnetically actuated switches have not been satisfactory heretofore for opening electrical circuits including the mentioned high energy ohmic heating circuit, because they have required expensive maintenance. For example, they have been rated at 115 or 120 volts, and when their contacts have been disengaged, the electrical energy passing through their contacts has caused arcing, burning or melting of their contacts. This has also caused ionization of the air around the contacts or other etfects that have permitted the contacts to conduct current even after they have been disengaged. Thus the switches have also been slow acting. Additionally, the switches known heretofore have required relatively complicated, expensive or troublesome electronic components, or have required relatively expensive, complicated or dangerous explosive components.

In accordance with this invention, an electrical circuit is opened by a simple system in which a conventional electromagnetic coil breaks a conducting member in the circuit in a safe, quick-acting, trouble-free manner that prevents any acing, burning or melting of contacts or other switch components. More particularly, in one of its aspects, this invention contemplates a fast-acting electrical switch, comprising a thin metallic foil adapted to conduct large amounts of electrical energy in a circuit, a magnetic coil having a power source, and means for energizing said magnetic coil from said source so as to produce a first magnetic field and resultant eddy currents having second magnetic fields in said foil which are operable with said first held to rupture said foil suddenly and thereby rapidly to open said circuit.

'Iheabove and further novel features of the invention will appear more fully from the following detailed description when the same is read in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are not intended as a definition of the invention but are for the purpose of illustration only.

In the drawing where like parts are marked alike:

FIG. 1 is a partial top view of an embodiment of this invention;

FIG. 2 is a partial cross-section of FIG. 1 through II-II.

FIG. 3 is a partial top view of apparatus of FIG. 1 after the foil thereof has been ruptured;

FIG. 4 is a schematic drawing of a test circuit incorporating the switch of this invention; and

FIG. 5 is a schematic drawing of an actual oscilloscope which is graduated to indicate the opening operation time of the apparatus of this invention in the circuit of FIG. 4.

foil 31, and it is easy to 'work and inexpensive.

Referring now to FIG. 1, the switch 11 of this invention is shown in one advantageous embodiment as it is useful for opening a high energy circuit for the ohmic heating of plasma in plasma research reactors or stellarators. Such reactors are described in US. Patents 2,910,- 414 and 3,002,912 and co-pending US. application Serial Number 688,089, now Patent No. 3,016,341, which is assigned to the assignee of this invention, and which relates particularly to ohmic heating coils for heating a plasma to high temperatures. It is understood, however, that the switch of this invention is useful in any other application where a fast-a-cting switch is required and is particularly advantageous where it is necessary suddenly to switch off high voltages without any arcing, melting or burning of contacts in a simple, inexpensive, safe and troublefree manner.

In accordance with this invention, leads 13 and 15 connect the input and output terminals (not shown) of a standard energy source 17, such as a high voltage source for ohmic heating coils (not shown) in a stellarator which requires up to 1000 amperes or more. Suitable means such as soldered joints connect the leads to terminals 23 and 25 at one end of the terminals. The other ends of the terminals accommodate holes 26 and 2.7 in the ends of metallic foil 31 which friction fits against the terminals 23 and 25 and against an insulating block 33' through which the terminals 23 and 25 pass. This friction fit with the terminals completes a circuit from source 17 to lead 13, to foil 31, to lead 15 and back to source 17 through which a high energy circuit passes from source 17.

Advantageously, the foil 31 is held evenly adjacent coil 34 and to this end the foil 31 has a uniform thickness and width, is evenly held under at least a hand tight tension between terminals 23 and 25 and is closely adjacent one side of coil 34. The foil 31 fits over terminals 23 and 25 which extend a short distance above the flat surface 35 of block 33, so as to provide the necessary tension. To this end the terminals are separated slightly relative to the holes 26 and 27 in the foil. This also centers the narrow portions 43 and 45 of foil 31 adjacent an end winding of coil 34 by centering hole 47 in the foil over the core 50 of coil 34. Suitable dimensions for a foil 31 adapted to carry 1000 amperes, include a foil 31 with a .004 inch thickness, one inch width, one and one-quarter inch lengths and one-half inch hole 47. Commercially available, aluminum foil has been found to be eifective, for Other suitable materials, however, include other high melting materials such as silver, copper and other metals that have sufiicient current carrying capacity as described above and a good capacity for magnetically induced eddy currents therein and magnetic tieldsassociated therewith as will be understood in more detail hereinafter.

Coil 34 advantageously is commercially available and has windings adapted to carry high voltages. A suitable coil would be a 10-30 turn single layer coil with an CD. of 1%" adapted to carry up to about 10,000 volts. The coil 34 is advantageously encapsulated in a regular moldable plastic block 33 of insulation with the coil core 50 coaxially corresponding with the foil hole 47. The block 33 thus insulates the foil 31 from the coil and evenly holds the coil 34 at a predetermined small distance from i the narrow portions 43 and 45 of foil 31. The insulation scope trace shown in FIG. 5. trace, a'D.-C. battery level was produced by battery 71 success ing material and the like which the coil 34 may be inserted.

Power source 61 comprises a suitable high energy capacitorbank which energizes coil 34 at predetermined intervals through a suitable low voltagejswitch 63 which increases the voltage on coil 34 rapidly. Such a switch. is provided by a gas-filled thyratron tube 63. To this end, leads 65 and 65" connect the power source 61 with 'coil 34 through thyratron 63 and a suitable mechanical switch 65 connected to low voltage source 67 biases the thyratron grid above cut-off until it is desired to energize coil 34. Then the disengagement of the contacts of switch 65 lowers the bias of the thyratron grid below cut-off, the thyratron 63 fired land the capacitor bank 61 'rapidly energizes coil 34. This produces astrong rapidly increasing first magnetic field around coil 34, in

which foil 31 is immersed, and strong increasing eddy currents having second magnetic fields in narrow portions 43 and 35 of foil 31 at an angle to the first field.

thereof to fire switch 63. This causes capacitor bank 61 rapidly to discharge through coil 34 and to immerse foil 31 in a strong increasing magnetic field produced by the 'coil 34-. This first field produces strong increasing eddy currents in narrow portions 43 and 45 in foil 34 which in turn produce corresponding fields around these eddy currents at an angle to the first field produced by coil 34. The first and second fields violently interact in operable association with the foil 31 rapidly and safely to rupture the foil across narrow portions 43 and 45 at relatively low temperatures. Tests have shown, for example, that the temperature of the foil'is only raised from room temperature to about 100 F. when 10,000 volts are discharged through coil 34and foil 31 has been conducting 1000 amperes. Moreover, tests with stellarator ohmic heating coils have shown that this invention is fast acting with high melting foils and this foil 31 has been ruptured rapidly in accordance with this invention by physical tearing without any detectable arcing or burning under the given conditions. Actual tests have also shown that the foil 31 has been ruptured in 100112 microseconds as shown by the schematic diagram of an oscillo- In connection with this ('FIG. 4) which conducted current through foil 31 and the trace was graduated in microseconds to show the time vs. voltage characteristics of this battery current through the foil when the foil was broken by the energization of foil 34. After the foil is broken, a new foil'is placed between terminals 23 and 25 and another cycle of operation is begun as described above. V

The foregoing has described an'improved fast-acting switch which is capable of openinga circuit rapidly with a sharp cut-off. Moreover, the described novel switch has the advantages of providing safe, dependable, inexperb' I ducting means bridging a gap in a circuit adapted to carry large amounts of electrical power, means for inducing eddy currents in said conducting means comprising magnetic means adjacent said conducting means, a source of power and means for connecting said source to said magnetic means to establish a magnetic field and induce eddy' currents in said'conducting means which suddenly l ruptures said conducting means and thereby rapidly breaks the connection across said gap in said circuit.

2. A fast-acting electric switch, comprising a high energy circuit in which there is a gap, a thin foil bridging said gap so as to complete said circuit, means for induc ing eddy currents in said foil comprising a magnetic. coil adjacent said foil, a source of power and means for connecting said source to said coil to establisha magnetic field and induce eddy currents in said foil thatinteract suddenly to rupture said foil and thereby rapidly to break said circuit inthe connection across said gap.

3. A fast-acting electric switch, comprising high energy leads between which there is a gap, thin foil of uniform thickness bridging said gap so as to conduct current between said leads, means for inducing eddy currents in said foil, comprising a magnetic coil adjacent said foil, an insulation disposed between said coil and said foil, and means for energizing said coil with sufficient current to produce magnetic fields andeddy currents in said foil that interact suddenly to rupturesaid'foil and thereby rapidly to break the conduction of current across said gap.

4. A fast-acting electric switch, comprising high energy leads between which there is a gap, a thin aluminum,

foil of substantially uniform thickness bridging said gap so as to conduct high energy between said leads, and means for inducing ed dy'currents in said foil, comprising a magnetic coil adjacent said :lio il, insulating means separating said coil and'foil, and means for energizing said coil with sufficient increasing current to produce a first increasing magnetic field around said coil, increasing eddy currents in said foil and second increasing magnetic'fields around said eddy currents which interact with said first field to rupture said foil in about microseconds and thereby suddenly to break the conduction of current across said gap. V i 1 5. A fast-acting electric switch, comprising high energy leads between which there is a gap, a thin metallic foil of substantially uniform thickness which connects "said leads so as to conduct high energy across said gap,

and means for inducing eddy currents in said foil, com prising a magnetic coil adjacent said foil, insulating means incapsulating said coil and holding said leads spaced apart, means for energizing said coil with sufliciently increasing current to produce a-first increasing magnetic field adjacent said coil, increasing eddy currents in said foil, and second increasing magnetic fields around said eddy currents which interact with saidfirst fields suddenly to rupture said foil and thereby suddenly to break the conduction of high energy across said gap.

6. A fast-acting electric switch, comprising high energy leads, a thin metallic foil of substantially uniform narrow portion of said foil, and means for energizing said coil with a sudden sufficiently increasing electrical current suddenly torupture .said foil. s

8. A fast-acting switch, comprising two high energy leads, having a first high energy source connected thereto,

' a thin metallic foil having narrow portions around a hole in said foil, said. foil connected between said leads, and

.means inducing eddy currents in said foil, comprising a-magnetic coil having a core that is coaxial ,Withthe hole in saidfoil, and windings that are adjacent said narrow portions of said foil, having a second high energy source and a quick-acting switch for connecting said second source to said coil.

9. A fast-acting electric switch, .comprising two high energy leads having a first high energy source connected quick-acting switch for connecting said second source to thereto, a thin metallic foil having a hole and narrow said coil.

portions at the edge of the hole, and means inducing eddy currents in said foil, comprising a magnetic coil having Refemmes flied 111 file 0f thls Patent windings forming a core that is coaxial with the hole in 5 UNITED STATES PATENTS said foil, means holding the ends of said foil in contact with said leads and the narrow portions of said foil under gg 68 52 53: tension evenly adjacent one side of said coil, a thin magg netic field permeable insulation interposed between said EIGN A NTS coil and said foil, 21 second high energy source, and a 10 7 9 9 Great Britain May 12 1927 

1. A FAST-ACTING ELECTRIC SWITCH, COMPRISING A THIN CONDUCTING MEANS BRIDGING A GAP IN A CIRCUIT ADAPTED TO CARRY LARGE AMOUNTS OF ELECTRICAL POWER, MEANS FOR INDUCING EDDY CURRENTS IN SAID CONDUCTING MEANS COMPRISING MAGNETIC MEANS ADJACENT SAID CONDUCTING MEANS, A SOURCE OF POWER AND MEANS FOR CONNECTING SAID SOURCE TO SAID MAGNETIC MEANS TO ESTABLISH A MAGNETIC FIELD AND INDUCE EDDY CURRENTS IN SAID CONDUCTING MEANS WHICH SUDDENLY RUPTURES SAID CONDUCTING MEANS AND THEREBY RAPIDLY BREAKS THE CONNECTION ACROSS SAID GAP IN SAID CIRCUIT. 